1. Technical Field of the Invention
This invention relates to hydroxy terminated polyamides and to the method by which they are prepared.
More particularly, this invention relates to polyoxypropylene polyamides terminated with primary hydroxyl groups which are useful in the preparation of polyurethanes having improved chemical resistance that can be used in lining blankets and clothing, as filters, as headliners for automobiles, etc. Still more particularly, this invention relates to hydroxy terminated polyamides having the formula: ##STR2## wherein:
a) R represents an aliphatic hydrocarbon group containing from 3 to about 34 carbon atoms or an aromatic group containing from 6 to about 34 carbon atoms,
b) R' represents an oxypropylene group having the formula: ##STR3## wherein n is a positive number having a value of 2 to about 15, and
c) R" represents an oxypropylene group having the formula: ##STR4## wherein n' is a positive number having a value of 15 to about 50, and
d) R'" represents an oxyethylene group having the formula: ##STR5## wherein n" is a positive number having a value of 1 to 4.
In accordance with another embodiment, the present invention is directed to a method for preparing hydroxy terminated polyamides wherein a molar excess of a dicarboxylic acid component is reacted with a diamine mixture composed of a higher molecular weight polyoxypropylene diamine and a lower molecular weight polyoxypropylene diamine, all as hereinafter defined, to provide a dicarboxylic acid polyoxypropylene polyamine intermediate which is reacted with an oxyethylene amino alcohol, as hereafter defined, in order to provide the desired hydroxy terminated polyamide.
2. Prior Art
The earliest polyurethane developments involved polyester polyols (see E. Muller, Rubber Plastics Age 39, 155 (1958). Polyethylene adipate was an early choice. It is a hard crystalline wax. The inherent crystallinity is the cause of spontaneous crystallinity of polyurethane rubbers made using this product. Poly-1,2-propylene adipate is a liquid which gives non-crystallizing rubbers that are considerably weaker than those from polyethylene adipate. A blend of 70 parts polyethylene adipate and 30 parts polypropylene adipate gives elastomers with good properties while the tendency to crystallize is largely suppressed. Further developments resulted in the products derived from diethylene glycol and adipic acid. This combination along with the addition of small amounts of other diols and triols such as trimethylol propane led to the polyesters used today in the preparation of polyester-based polyurethanes.
The major drawback of polyester based polyurethanes is their hydrolytic instability (see Athey, R. J., "Water Resistance of Liquid Urethane Vulcanizates", Rubber Age 96, 5(1965) 705-712). Athey found that with prolonged exposure under severe conditions of high humidity polyesters were severely degraded, whereas polyethers held their properties well. He also performed experiments in wet and dry oil. When moisture was present in the oil, the polyesters degraded very badly. Polyether based foams suffered only slightly. The polyester linkage was the point of attack. Although polyesters have been replaced by polyethers in most flexible foam markets, polyester based polyurethanes have an important place in the polyurethane economy. The polyester urethanes can be flame laminated and show good chemical resistance. They are used in lining in blankets and clothing, for filters and headliners for automobiles. These uses along with the fact that they can be formulated to provide some fire-retardancy explain the interest held in flexible polyurethane foams based on polyesters. Hydroxy-terminated polyesters based on dimer acids have been made. Foams prepared from dimer acid polyesters show improved hydrolytic stability over those made from adipate polyesters. This is because the dimer acid based products are more hydrophobic in nature and contain a lower weight percentage of ester groups. Flexible foams made from dimer acid esters have excellent properties. Polyurethane Foams Technology, Properties and Applications, by Arthur H. Landrock, Plastic Report, 37, January 1969, p. 18.